Gear shifting transmissions of motor vehicles are usually controlled or shifted using an actuating device disposed within reach of the driver. Actuating elements such as shift levers or selector levers are used customarily for this purpose, and are disposed between the front seats of the motor vehicle, for example.
The structural and ergonomic requirements on actuating devices of this type for gear shifting transmissions are diverse. For example, to provide the driver with a realistic feel for the actuation of the transmission for reasons of safety and ergonomics, a requirement of actuating devices is that the driver, when selecting a gear, be provided with clear haptic or tactile feedback about the current gear state or operating state of the transmission. Based thereon, the driver should be able to deduce the shifting operation that actually took place in the transmission when he operates the selector lever. Likewise, it should be possible for the driver to intuitively understand the current gear state of the transmission by glancing at the selector lever or by grasping the selector lever.
It is therefore desirable to provide the driver with clear visual and haptic feedback about the current transmission state or the actual gear selection position that is engaged on the basis of the particular position or angular position of the selector lever at the moment.
In the case of classical, mechanical transmission control or mechanical coupling between the selector lever and the gear shifting transmission—using a cable or linkage, for example—the selector lever position always coincides with the actual transmission position due to the mechanical coupling. Since mechanically actuated gear shifting transmissions themselves are generally multistable (that is, the transmission shifting position is stable in a plurality of positions or in all positions), the associated selector lever is likewise multistable and therefore always remains, as does the gear shifting transmission, in the position or gear selected by the driver.
As a result, the driver can deduce, on the basis of the particular selector lever position, the current gear state of the transmission, and, on the basis of the selector lever position, he can determine the gear selection position that is engaged in the transmission; the driver can feel confident that the selector lever position coincides with the actual gear state of the transmission.
However, when gears are shifted electrically, which is becoming increasingly more common, that is, when gear shifting transmissions are actuated using shift-by-wire controls, the selector lever in the passenger compartment and the motor vehicle transmission in the engine compartment are usually not mechanically coupled. Instead, in the case of shift-by-wire-controlled transmissions, the shift commands are usually transmitted from the actuating device to the motor vehicle transmission nearly exclusively via electrical or electronic signals, and the shift commands are then implemented in the transmission using an electrohydraulic system. This applies to a partial extent to modern manual transmissions, but in particular to the current generations of automatic transmissions that are generally entirely remote-controlled using actuators.
In shift-by-wire gear shifting transmissions, however, the absence of a mechanical connection between the transmission actuator system and the selector lever can, under certain basic conditions, lead to the selector lever position no longer coinciding with the gear state of the transmission.
For example, modern automatic transmissions usually include a so-called “Auto-P” function that ensures that, when the driver leaves the vehicle, the parking lock may possibly be engaged automatically in the transmission to prevent the unattended vehicle from rolling away if the driver failed to engage the parking lock before he left the vehicle. In other words, the Auto-P function, which is always automatically activated ensures that when the ignition key is removed or the driver leaves the vehicle, the parking lock is automatically engaged in the transmission, regardless of which gear selection position was actually selected using the selector lever. For example, the parking lock is engaged automatically by the Auto-P function of the transmission or the vehicle whenever the driver leaves the selector lever in the neutral position, in a tip gate that may be present, or in one of the gear selection positions.
In this case however, the selector lever position does not coincide with the actual gear state of the transmission. When the driver would return to the vehicle or attempt to start the vehicle, the position of the selector lever would therefore provide the driver—visually and haptically—with incorrect information. On the basis of his perception of the selector lever position, the driver would have to assume that the transmission is engaged in a neutral position or in a gear selection position, although the transmission is actually engaged in the parking lock. To prevent the driver from being misinformed in this manner, an additional signaling device would therefore have to be provided especially for the driver, that, if the parking lock had been engaged by Auto-P, would signal to the driver that the selector lever must first be moved manually into the parking lock position and, therefore, in conformance with the actual gear state of the transmission, before the vehicle can be started.
An attempt is made in the prior art to address the problems presented herein by designing the selector lever of shift-by-wire gear shifting transmissions as monostable actuating elements. This means that a monostable selector lever of this type always returns to the same center position after it has been actuated. Thus, in the case of a monostable selector lever, the communication regarding the actual gear state of the transmission is left exclusively to a separate display, for example using light-emitting diodes. When a monostable selector lever is utilized, however, the driver is unable to obtain visual or haptic feedback about the gear state of the transmission based on the position of the selector lever. Furthermore, the implementation of the mechanical shift logic and the necessary shift interlocks—such as the so-called “key lock” and “shift lock” interlocks, for example—in monostable selector levers is often complex and requires a complicated actuator system to selectively block impermissible shift commands depending on the driving condition of the motor vehicle; this is structurally complex and correspondingly costly.
The known monostable actuating devices also have the disadvantage that the driver must become familiar with a new operating concept that includes a lever that always aims to return to the center position, wherein this operating concept differs considerably from traditional transmission actuation using stable selector lever positions.